Process for regenerating spent heavy hydrocarbon hydroprocessing catalyst

ABSTRACT

The present invention relates to a spent hydroprocessing catalyst regeneration process wherein the catalyst is subjected to an initial partial decoking step, followed by impregnation with a Group VIB metal-containing component, and then subjected to a final decoking step.

BACKGROUND OF THE INVENTION

The United States and Canada generate about 100,000,000 pounds of spentbase-metal catalyst per year, about half of which is spenthydroprocessing catalysts. The present invention relates to a processfor regenerating spent heavy hydrocarbon hydroprocessing catalysts. Morespecifically, the present invention relates to a process forregenerating spent heavy hydrocarbon hydroprocessing catalysts that havebeen deactivated with coke and metal deactivants such as nickel andvanadium.

With respect to the present invention, the term hydroprocessing is usedto refer to a process for hydrodemetallation, hydrodesulfurization,hydrodenitrogenation, and hydroconversion wherein the termhydroconversion encompasses the hydrocracking and hydrotreating ofhydrocarbon streams containing asphaltenes and contaminant metals.Hydroprocessing catalysts used to treat heavy hydrocarbon streams, suchas resids, are deactivated as a result of metals deposition and cokedeposition. These deposition materials modify the rate of reaction aswell as accelerate the rate of catalyst deactivation. The various metaldeposits tend to occlude catalyst pores and poison the hydroprocessingcatalyst, while coke deposits similarly reduce pore size and surfacearea of the hydroprocessing catalyst.

Typically, hydroprocessing catalysts possess substantial macroporevolume in order to effect metals removal from the heavy hydrocarbon feedstreams. Heavy hydrocarbon hydroprocessing catalysts possess thecapacity to adsorb contaminant metals, such as nickel and vanadium, inan amount ranging up to about 100 wt.% of the fresh catalyst weight.However, due to the rapid coke deposition rate, the catalyst isdeactivated prior to achieving its full metals adsorption capacity. Suchcatalysts are taken out of service when they contain as little as 10wt.% nickel plus vanadium. If the spent catalyst is not regenerated, itis subsequently sent to a metals reclamation facility where the proceedstherefrom, in part, depend upon the vanadium content of the spentcatalyst.

Thus, the prior art is replete with processes suitable for regeneratingor rejuvenating such hydroprocessing catalysts. In general, theseprocesses involve removing the deposited contaminant metals, preceded orfollowed by a coke burn-off step. The metals can be removed first, forexample, by acid-leaching with oxalic acid or sulfuric acid, followed bythe decoking step. While some processes afford the extraction of nickeland vanadium without removing active metals [U.S. Pat. No. 4,677,085(Nevitt)], catalytic metals such as cobalt and molybdenum may have to bereimpregnated (Silbernagel, B. G., R. R. Mohan, and G. H. Singhal, "NMRStudies of Metal Deposition on Hydroprocessing Catalysts and Removalwith Heteropolyacids," ACS Div. Ind. Eng. Chem. Catal. Mater.Relationship Struct. Reactivity Symposium (San Francisco 6/13-16/83) ACSSymp. Ser. 248, 91 (1984)).

In the fluidized catalytic cracking (FCC) art, feedstocks containingvanadium are handled by the use of passivation agents. For instance,U.S. Pat. No. 4,451,355 (Mitchell et al.) discloses the use of calcium,antimony, tin, barium, manganese, and bismuth additives to mitigate thepoisonous effects of nickel, vanadium and iron contained in FCCfeedstocks. U.S. Pat. No. 4,364,847 (Tu) discloses the use of lithium tocarry out the subject pacification.

Similarly, U.S. Pat. No. 4,549,958 (Beck et al.) discloses treatment ofhydrocarbon oil having a significant content of vanadium. A fluidizablesorbent is used to demetallize and decarbonize the hydrocarbon oil. Thesorbent contains additive metal components in an amount sufficient tocomplex with and immobilize the flow characteristics of sodium vanadatesor vanadium pentoxide formed during the sorbent oxidative regenerationstep. These additive metals are selected from the group consisting ofMg, Ca, Ba, Sc, Y, La, Ti, Zr, Hf, B, Ta, Mn, In, Te, an element in thelanthanide or actinide series, or an organo-metallic compound of theadditive metal component.

As mentioned above, the metals, especially vanadium, tend to deactivatehydroprocessing catalysts; however, these metals also tend to affect thecatalyst's physical properties, such as the crush strength and theattrition rate of a regenerated hydroprocessing catalyst. Further, mostregeneration processes achieve only partial or mixed restoration offresh activities regardless of whether the contaminant metals areremoved. In this connection, the paper "Studies of Poisoning andRegeneration of Hydrodesulfurization and Hydrodemetallization Catalystduring Treatment of Venezuelan Crude Oils" J. Japan Petrol. Inst.22,(4), 234-242 (1979) shows that where catalysts have been used inhydrodesulfurization (HDS) and hydrodenitrogenation (HDN) processes totreat Venezuelan feeds, the activity loss could only be regenerated byabout 70 to 90 percent because vanadium deposits modified the activitystrongly by blocking catalyst pores and active centers.

In ACS Div. of Petroleum Preprints Vol.27 No.3 679-81 (Sept. 1982), aprocess is disclosed wherein a commercial Al-Co-Mo catalyst isregenerated using a solvent-extraction treatment to extract contaminantmetals with organic reagents capable of forming water-soluble metalcomplexes. The extraction step was followed by a coke burning step. Theregenerated catalyst possessed a lower hydrodesulfurization activity yeta higher hydrodevanadization activity.

U.S. Pat. No. 4,795,726 (Schaper et al.) discloses a method forregenerating spent alumina-based catalysts that have been employed intreating metals-contaminated hydrocarbon feedstocks. The subject processinvolves a steam treatment step, coke burn-off step, and a basic mediumtreatment step. The process may require the addition of catalytic metalsto the regenerated catalyst since the catalytic metals are removedtogether with the vanadium and nickel.

In a paper, Ernst W. R., et al. "GTRC Process For Removing InorganicImpurities From Spent Hydrodesulfurization Catalysts" Minerals andMetallurgical Processing, 4 (2), 78 (1987), a method is disclosed forremoving nickel and vanadium contaminants from spenthydrodesulfurization catalysts that involves pretreating the catalystwith H₂ S followed by the extraction of nickel and vanadium with anacidic solution of ferric ion. The subject method results in the removalof some catalytic metals, such as 50 percent of the cobalt and 5 percentof the molybdenum. The regenerated catalyst possessedhydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities ofabout 70 percent of the fresh catalyst activities, while thedeactivation rates, for HDS but not HDN of the regenerated catalyst weresuperior to those of the fresh. The regenerated catalyst possessedsuperior hydrodemetallation activity.

Various additives or reagents have been employed to assist in theregeneration of hydroprocessing or hydrorefining catalysts. Forinstance, U.S. Pat. No. 4,581,129 (Miller et al.) discloses a processfor regenerating a hydrorefining catalyst which results in restorationof catalytic activity, no loss in the strength of the support material,and no unacceptable loss of active metals. The subject patent disclosesan embodiment of the invention wherein a mild heat treatment or apartial decoking step is preceded or immediately followed by anextraction of the vanadium and nickel metal contaminants with an acidicsolution. A preferred metals-extraction method is disclosed in U.S. Pat.No. 4,089,806 (Farrell et al.) wherein oxalic acid or in one or morewater-soluble, nitrate-containing compounds, such as nitric acid, andwater-soluble inorganic nitric salts are used. The subject regenerationprocess involves incorporating a phosphorous component after the partialdecoking and extraction step prior to combusting essentially theremainder of the coke from the catalyst.

The subject patent offers the explanation that carrying out the decokingin the absence of phosphorous by combustion releases SO₂ from the sulfuron the catalyst, which SO₂, in the presence of O₂, and the largequantities of vanadium contaminants on the catalyst, are partiallyconverted to SO₃. During combustion, the SO₃ reacts with the aluminacomponent of the hydrorefining catalyst to form aluminum sulfate, and,as a result, the crushing strength, pore volume, surface area, andactivity of the catalyst are often reduced. The subject patent furtherexplains that vanadium on the deactivated catalyst is initially in the+3 or +4 oxidation state in such forms as V₂ S₃ or VS₂. Thus, when asufficient temperature threshold is surpassed, the vanadium is convertedto the +5 oxidation state suitable for promoting the SO₂ conversion toSO₃. Incorporation of phosphorous components with the deactivatedcatalyst is thought to passivate or inhibit, by some chemical reactionmechanism, the vanadium conversion to the +5 oxidation state and therebyinhibit the sulfation mechanism.

The Patentees also point that their metals-extraction process may resultin a reduction of MoO₃ and CoO catalytic components, e.g., from 12 and 4wt.% to 8 and 3 wt.%, respectively. Thus, Patentees suggest in a highlypreferred embodiment of their invention, that catalytic components bereintroduced to the rejuvenated catalyst. Patentees also suggest thatthe rejuvenated catalyst be crushed and reformulated into particulateform by extruding a mixture of a gel and the crushed rejuvenatedcatalyst.

U.S. Pat. No. 4,089,806 (Farrell et al.) as mentioned above alsodiscloses a process for removing vanadium and nickel deactivants fromcontaminated hydrodesulfurization catalysts comprising Group VIB and/orGroup VIII active components on refractory oxide supports. In thisprocess, the spent catalyst is contacted with an aqueous regenerantsolution comprising oxalic acid and one or more solublenitrate-containing compounds from the class consisting of nitric acidand water-soluble inorganic nitrate salts. Suitable nitrate saltsinclude sodium nitrate, ammonium nitrate, potassium nitrate, calciumnitrate, magnesium nitrate, copper nitrate, etc., with the preferredsalt being aluminum nitrate. This contacting results in the removal ofvanadium and nickel contaminants from the surface of the deactivatedcatalyst and substantially rejuvenates the catalyst forhydrodesulfurization purposes, provided that such removal isaccomplished prior to the burning off of any coke present in thecatalyst.

The patent further maintains that subsequent decoking after thecontacting treatment with the regeneration solution is optional.Sufficient activity is restored by the method described without decokingbeing necessary. Patentees maintain that decoking of heavily deactivatedcatalyst may actually result in a loss of some of the activity restoredby the treatment with the regenerant solution. Patentees furthermaintain that it is a critical aspect of the invention that thedeactivated catalyst should not be decoked prior to treatment withregenerant solution, primarily because such decoking is generallycounterproductive. Decoking by combustion prior to the treatmentdescribed herein releases SO₂ from the sulfur in the coke which, in thepresence of O₂ and large quantities of vanadium, deactivates thecatalyst. The so-produced SO₃ then reacts with the alumina catalystsupport to form aluminum sulfate, thereby lowering the crush strength.

Farrell et al. maintain that the rejuvenated catalyst will have at least30 percent, usually 70 percent and an occasion over 80 percent of thefresh original activity. Patentees explain that full restoration isgenerally not possible since 10 percent or less of the active catalyticcomponents are removed from the catalyst during the regenerationprocess.

U.S. Pat. No. 4,268,415 (Mohan et al.) discloses a process for theregeneration of spent hydrodesulfurization catalysts with heteropolyacids and hydrogen peroxide. In particular, the patent discloses aprocess wherein a spent hydrofining catalyst is regenerated bycontacting the spent catalyst with a solution of a heteropoly acidhaving the general formula of H_(x) (YM₁₂ O₄₀) where Y is at least oneelement selected from the group consisting of phosphorus, silicon,titanium, germanium, arsenic, zirconium, thorium and cerium, M is atleast one element selected from the group consisting of molybdenum,tungsten, niobium and tantalum and x is 3 when Y is pentavalent (P, As)and x is 4 when Y is tetravalent (Si, Ti, Ge, Zr, Ce, Th). Theheteroploy acid solution preferably contains 1 to 50 wt.% hydrogenperoxide. Patentees maintain that the method results in the extractionof about 70 to 100% vanadium and about 90% nickel and about 50% cobaltwith essentially no loss of molybdenum and aluminum coupled with thepreservation of the structural integrity of the catalyst support. Thespent catalyst regeneration process can also further include additionalprocessing by doping the demetallized catalyst with cobalt followed bycalcination. The subject cobalt impregnation improves or promotes carbondecoking, further sulfur removal, and an additional increase in surfacearea and pore volume. Patentees maintain that hydrorefining activity andproduct selectivity of the regenerated spent catalyst is substantiallythe same as that of the fresh catalyst.

U.S. Pat. No. 4,728,417 (Aldag, Jr. et al.) discloses a process whereinan additive comprising a mixture of at least one decomposable molybdenumcompound selected from the group consisting of molybedenumdithiophosphates and molybdenum dithiocarbamates and at least onedecomposable nickel compound selected from the group consisting ofnickel dithiophosphates and nickel dithiocarbamates is mixed with thehydrocarbon feed. The hydrocarbon feed containing the additive is thencontacted with the hydrofining catalyst. The additive can be added whenthe catalyst is new, partially deactivated or spent with a beneficialresult occurring in each case. Patentees maintain that the introductionof the additives slows down the catalyst rate of decline from the timeof introduction and in some cases improves at least a partially spent ordeactivated catalyst from the time of introduction.

Accordingly, the prior art presents a dilemma in that contaminant metalsmust be removed to retain or restore physical and catalytic propertiesof the spent hydroprocessing catalyst, yet its reclamation value isdiminished when the metal, i.e., vanadium, content of the spent catalystis reduced. Thus, there is a need for a catalyst regeneration processwherein the catalyst poisoning contaminant metals, such as vanadium,need not be removed such that the demetallization capacity of thehydroprocessing catalyst is entirely utilized thereby increasing itseventual reclamation value. Further, there is a need for a regenerationprocess that restores all catalytic activities without the need toreimpregnate catalytic metals while concomitantly maintaining requisitephysical properties such as attrition resistance, attrition resistancebeing an especially important property when the catalyst is employed inan ebullated bed reactor system.

It has now been discovered that when a Group VIB metal component isincorporated into the spent catalyst in accordance with the presentinvention, catalyst activities can be restored with no need for removalof contaminant metals coupled with no loss in catalyst attritionresistance.

SUMMARY OF THE INVENTION

The present invention relates to a process for regenerating a spentheavy hydrocarbon hydroprocessing catalyst. Specifically, the processincludes the steps of carrying out an initial partial decoking stepwherein the spent catalyst is contacted with an oxygen-containing gas atabout 400° F. to about 700° F. At least one Group VIB metal is thenincorporated with the partially decoked catalyst in an amount such thatthe partially decoked catalyst contains about 0.1 to about 20.0 wt.% ofthe Group VIB metal calculated as the oxide. The impregnated catalyst isthen subjected to another final decoking step in the presence of anoxygen-containing gas at about 600° F. to about 1,400° F.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 4 depict plots of hydrodesulfurization activity,hydrodenitrogenation removal activity, Ramscarbon removal activity, anddevanadation activity, respectively, versus weight percentageaccumulation of nickel plus vanadium for both comparative and inventioncatalysts tested in the Example 1.

DETAILED DESCRIPTION OF THE INVENTION

Broadly, the present invention is directed to the regeneration ofcatalysts used in a process for the hydroprocessing of heavy hydrocarbonfeedstocks which contain asphaltenes, Shell hot filtration solidsprecursors, metals, nitrogen compounds, and sulfur compounds. As is wellknown, these feedstocks contain nickel, vanadium, and asphaltenes, e.g.,about 40 ppm up to more than 1,000 ppm for the combined total amount ofnickel and vanadium and up to about 25 wt.% asphaltenes. These catalystshave been used in processes that treat feedstocks with a substantialamount of metals containing 150 ppm or more of nickel and vanadium andhaving a sulfur content in the range of about 1 wt.% to about 10 wt.%.These catalysts have been used to treat feedstocks that contain asubstantial amount of components that boil appreciably above 1,000° F.Examples of typical feedstocks are crude oils, topped crude oils,petroleum hydrocarbon residua, both atmospheric and vacuum residua, oilsobtained from tar sands and residua derived from tar sand oil, andhydrocarbon streams derived from coal. Such hydrocarbon streams containorgano-metallic contaminants which create deleterious effects in variousrefining processes that employ catalysts in the conversion of theparticular hydrocarbon stream being treated. The metallic contaminantsfound in such feedstocks include, but are not limited to, iron,vanadium, and nickel.

Nickel is present in the form of soluble organo-metallic compounds inmost crude oils and residuum fractions. The presence of nickel porphyrincomplexes and other organo-nickel complexes causes severe difficultiesin the refining and utilization of heavy hydrocarbon fractions, even ifthe concentration of such complexes is relatively small. It is knownthat a cracking catalyst deteriorates rapidly and that its selectivitychanges when in the presence of an appreciable quantity of theorgano-nickel compounds. An appreciable quantity of such organo-nickelcompounds in feedstocks that are being hydrotreated or hydrocrackedharmfully affects such processes. The catalyst becomes deactivated, andplugging or increasing of the pressure drop in a fixed-bed reactorresults from the deposition of nickel compounds in the intersticesbetween catalyst particles.

Iron-containing compounds and vanadium-containing compounds are presentin practically all crude oils that are associated with the highConradson carbon asphaltenic and/or asphaltenic portion of the crude. Ofcourse, such metals are concentrated in the residual bottoms when acrude is topped to remove those fractions that boil below about 450° F.to 600° F. If such residuum is treated by additional processes, such asfluidized catalytic cracking, the presence of such metals as well assulfur and nitrogen adversely affects the catalysts in such processes.It should be pointed out that the nickel-containing compoundsdeleteriously affect cracking catalysts to a greater extent than doiron-containing compounds. If an oil containing such metals is used as afuel, the metals will cause poor fuel oil performance in industrialfurnaces since they corrode the metal surfaces of the furnaces.

While metallic contaminants, such as vanadium, nickel, and iron, areoften present in various hydrocarbon streams, other metals are alsopresent in a particular hydrocarbon stream. Such metals exist as theoxides or sulfides of the particular metal, or as a soluble salt of theparticular metal, or as high molecular weight organo-metallic compounds,including metal naphthenates and metal porphyrins and derivativesthereof.

It is widely known that various organometallic compounds and asphaltenesare present in petroleum crude oils and other heavy petroleumhydrocarbon streams, such as petroleum hydrocarbon residua, hydrocarbonstreams derived from tar sands, and hydrocarbon streams derived fromcoals. The most common metals found in such hydrocarbon streams arenickel, vanadium, and iron. Such metals are very harmful to variouspetroleum refining operations, such as hydrocracking,hydrodesulfurization, and catalytic cracking. The metals and asphaltenescause interstitial plugging of the catalyst bed and reduced catalystlife. The various metal deposits on a catalyst tend to poison ordeactivate the catalyst. Moreover, the asphaltenes tend to reduce thesusceptibility of the hydrocarbons to desulfurization. If a catalyst,such as a desulfurization catalyst or a fluidized cracking catalyst, isexposed to a hydrocarbon fraction that contains metals and asphaltenes,the catalyst will become deactivated rapidly and will be subject topremature replacement.

Although processes for the hydroprocessing of heavy hydrocarbon streams,including but not limited to heavy crudes, reduced crudes, and petroleumhydrocarbon residua, are known, the use of fixed-bed catalytic processesto convert such feedstocks without appreciable asphaltene precipitationand reactor plugging and with effective removal of metals and othercontaminants, such as sulfur compounds and nitrogen compounds, is notcommon because the catalysts employed have not generally been capable ofmaintaining activity and performance.

Thus, the subject hydroprocessing processes are most effectively carriedout in an ebullated bed system. In an ebullated bed, preheated hydrogenand resid enter the bottom of a reactor wherein the upward flow of residplus an internal recycle suspend the catalyst particles in the liquidphase. Recent developments involved the use of a powdered catalyst whichcan be suspended without the need for a liquid recycle. In this system,part of the catalyst is continuously or intermittently removed in aseries of cyclones and fresh catalyst is added to maintain activity.Roughly about 1 wt.% of the catalyst inventory is replaced each day inan ebullated bed system. Thus, the overall system activity is theweighted average activity of catalyst varying from fresh to very old,i.e., deactivated.

Typically, the subject hydroprocessing process is carried out in aseries of ebullated bed reactors. As previously elucidated, an ebullatedbed is one in which the solid catalyst particles are kept in randommotion by the upward flow of liquid and gas. This random motion makesthe attrition resistance of the catalyst a very important property.Attrition resistance is also an important property with respect tocatalysts employed in a fixed bed reactor, because the catalyst mustmaintain its physical integrity, i.e., resist attrition, while it isbeing loaded into a reactor.

In any event, an ebullated bed typically has a gross volume of at least10 percent greater and up to 70 percent greater than the solids thereofin a settled state. The required ebullation of the catalyst particles ismaintained by introducing the liquid feed, inclusive of recycle, if any,to the reaction zone at linear velocities ranging from about 0.02 toabout 0.4 feet per second and preferably, from about 0.05 to about 0.20feet per second.

The catalyst that is regenerated in accordance with the presentinvention preferably contains a hydrogenation component, a porousinorganic oxide support and is free from a molecular sieve component.

Preferred hydrogenation components are selected from the groupconsisting of Group VIB metals and Group VIII metals. The addition of aGroup VIII metal to the catalyst is especially useful when ebullated bedreactors are employed. In a fixed-bed reactor the activity of thecatalyst dissipates over time, whereas in the ebullated bed reactor,since fresh amounts of catalyst are continuously or intermittentlyadded, the Group VIII metal provides increased overall average activitysince the presence of a Group VIII promoter provides a higher initialactivity than the catalyst not containing such a promoter. The freshlyadded higher, initial activity catalyst is included in the weightedaverage used to determine overall average activity. It has beendiscovered that relatively small amounts of cobalt present in ahydroprocessing catalyst provide excellent hydroprocessing activity inan ebullated bed system. This low cobalt-containing hydroprocessingcatalyst is disclosed and claimed in U.S. Pat. No. No. 4,657,665 (Beatonet al.). This low cobalt-containing catalyst also has a Group VIB metalpresent in an amount ranging from about 3.5 to about 5.0 wt.% calculatedas an oxide and based on total catalyst weight. The cobalt is present inan amount ranging from about 0.4 to about 0.8 wt.% calculated as anoxide (CoO) and based on total catalyst weight.

In any event, the hydrogenation metals can be deposed on a porousinorganic oxide support such as alumina, aluminum phosphate, or aluminumsilicates. Suitably, the composition of the hydroprocessing catalyst ofthe present invention comprises from about 3.0 to about 15.0 wt.% of theGroup VIB metal, calculated as the oxide. Preferably, the Group VIBmetal is molybdenum. The Group VIB and Group VIII classifications of thePeriodic Table of Elements can be found on page 628 of Webster's SeventhNew Collegiate Dictionary, G. & C. Merriam Company, Springfield, Mass.,U.S.A. (1965). While calculated as the oxide, the hydrogenation metalcomponents of the catalyst can be present as the element, as an oxidethereof, as a sulfide thereof, or mixtures thereof. Molybdenum, which isgenerally superior to chromium and tungsten in demetallation anddesulfurization activity as mentioned above, is the preferred Group VIBmetal component in the demetallation catalyst.

The Group VIII metal can be present in an amount ranging from about 0.4to about 4.0 wt.% calculated as an oxide and based on total catalystweight. The preferred Group VIII metals are cobalt and nickel. Thecobalt and nickel are preferably present in an amount such that the CoOor NiO to Group VIB metal oxide weight ratio varies from about 0.2 toabout 0.3.

The hydroprocessing catalyst regenerated in accordance with the processof the present invention can be prepared by the typical commercialmethod of impregnating a large-pore, high-surface area, inorganic oxidesupport or any other method known to those skilled in the art.Appropriate commercially available alumina, preferably calcined at about800°-1,600° F. (426°-872° C.), for about 0.5 to about 10 hours, can beimpregnated to provide a suitable surface area ranging from about 75 m²/g to about 400 m² /g and a total pore volume within the range of about0.5 cc/g to about 1.5 cc/g.

Preferably, the surface area ranges from about 150 m² /g to about 350 m²/g, a total pore volume of about 0.8 cc/g to about 1.2 cc/g. Thecatalysts most suitably regenerated in accordance with the presentinvention contain pore volume of pores having a diameter greater than1,200 Angstroms of at least 0.05 cc/g, preferably at least 0.1 cc/g, andoptimally from about 0.15 to about 0.3 cc/g.

The porous refractory inorganic oxide, e.g., alumina can be impregnatedwith a solution, usually aqueous, containing a heat-decomposablecompound of the metal to be placed on the catalyst, drying, andcalcining the impregnated material. If the impregnation is to beperformed with more than one solution, it is understood that the metalsmay be applied in any order. The drying can be conducted in air at atemperature of about 80° F. (27° C.) to about 350° F. (177° C.) for aperiod of 0.1 to 5.0 hours. Typically, the calcination can be carriedout at a temperature of about 800° F. (426° C.) to about 1,200° F. (648°C.) for a period of from 0.5 to 16 hours.

Alternatively, the inorganic oxide support can be prepared by mixing asol, hydrosol, or hydrogel of the inorganic oxide with a gelling medium,such as ammonium hydroxide followed by constant stirring to produce agel which is subsequently dried, pelleted, or extruded, and calcined.The hydrogenation metal(s) can then be incorporated into the support asdescribed above or incorporated during the gelling step.

While the hydroprocessing catalyst regenerated in accordance with thepresent invention can be present in the form of pellets, spheres, orextrudates, other shapes are also contemplated, such as a clover-leafshape, cross-shape, or C-shape as disclosed in U.S. Pat. Nos. 3,674,680and 3,764,565 (Hoekstra, et al.).

As mentioned above, during use of the above-described catalysts, theireffectiveness is diminished because hydrocarbon residues in the form ofcoke and contaminant metals such as nickel and vanadium deposit andbuild up on catalyst surfaces and within catalyst pores. The term"contaminant metals" is used to designate metals incidentally compositedwith the catalyst. In some cases residues of the same metal which isused as a catalytic metal deposit incidentally as a contaminant metal onthe catalyst. Nickel is an example of a metal which may be both acatalytic metal and a contaminant metal. In this case the metalintentionally put on the catalyst as a catalytic metal remains"catalytic metal," and the same-metal residue incidentally depositedduring use of the catalyst becomes a "contaminant metal."

In any event, coke and contaminant metals build-up reduces catalystactivity and selectivity, thereby resulting in deactivated, or spentcatalyst. Catalyst activity is a measure of the catalyst's ability toassist the conversion of reactants into products at a specified severitylevel, where severity level means the reaction conditions used, that isthe temperature, pressure, contact time, and presence of diluents, ifany. Catalyst selectivity is a measure of the catalyst's ability to helpproduce a high amount of desired products relative to the amount ofreactants charged or converted.

The spent heavy hydroprocessing catalyst suitable for use in the presentregeneration invention usually contains a total contaminant metalsbuild-up of greater than about 4 wt.% nickel plus vanadium based onfresh catalyst weight. The carbonaceous or coke build-up ranges fromabout 20 to about 60 wt.% based on total fresh catalyst weight. Therelative amounts of metals and coke present in deactivated catalysts isdependent upon the relative upstream or downstream position of thecatalyst in the reactor while it is in use. The upstream catalyst wouldcontain more metals while the downstream catalyst would contain morecoke.

Prior to carrying out the process of the invention, the catalyst may beoptionally washed with an organic solvent such as toluene or strippedwith an inert gas to remove surface oils.

In accordance with the process of the present invention spent heavyhydroprocessing catalyst is initially subjected to a partial decoking oroxidation step wherein the catalyst is contacted with anoxygen-containing gas at about 400° F. to about 700° F. This partialdecoking step is carried out until up to about 70 weight percent of thedeposited carbonaceous material is removed. The theory behind thispartial decoking step which is not a limitation on the present inventionis that the macropores are sufficiently opened by coke burn-off withoutoxidizing the vanadium contaminants. The preferred gas comprises air andrecycled combustion gases.

Subsequent to the initial decoking step at least one Group VIB metal isincorporated with the partially decoked spent catalyst.

The Group VIB metal(s) can be incorporated into the partially decokedspent catalyst by any method known to those skilled in the art.Typically, the partially decoked spent catalyst can be impregnated toincipient wetness with an aqueous, or organic solution or dispersion ofa or compounds of the Group VIB metal(s).

Preferably, nitrates, carbonates and salts of organic acids, such asacetates are employed in the impregnating solution or dispersion. Theimpregnation solution should contain a sufficient amount of Group VIBmetal(s) such that the impregnated spent catalyst contains from about0.1 to about 20 wt.% of the Group VIB metal(s) calculated as theoxide(s) and based on fresh catalyst weight.

Preferably, the impregnating solution contains a sufficient amount ofGroup VIB metal(s) to result in an impregnated spent catalyst containing0.5 to 10.0 wt.% Group VIB metal calculated as the oxide(s) and based onfresh catalyst weight. Most preferably or optimally the subject catalystcontains from about 1.0 to 5.0 wt.% Group VIB metal(s) on theabove-described basis.

The preferred Group VIB metal is molybdenum. As mentioned, in part,above, the Group VIB metal(s) can be impregnated with aqueousimpregnating solutions that contain the Group VIB metal(s) as thesalt(s) of a nitrate, a sulfate, a sulfite, an acetate, a benzoate, ahalide, a carbonate, an oxy-halide, a hydroxide, an oxalate and athiosulfates. The impregnation can also be performed using organicsolvents (alcohols, ketones and esters) containing the above-mentionedcompounds.

While not wishing to be bound by theory, it is speculated that thecatalyst-softening or high attrition rate that occurs after conventionalregeneration processes can be attributed to the following mechanism.

When hydroprocessing catalysts are subjected to a combustion step in airunder conditions to remove coke, i.e., 900° to 1000° F., one of thespecies oxidized is the V₃ S₄ sulfide, the predominant vanadium phasedeposited under typical heavy hydrocarbon hydroprocessing conditions.The sulfide is then converted to an equilibrium mixture consisting ofthe V₂ O₅ pentoxide (penta-valent vanadium) as well as sub-oxides andoxy-sulfates (tetra-valent vanadium and lower).

Water formed during the combustion step reacts with the pentoxide toform vanadic acid, VO(OH)₃, a volatile and highly reactive species thatreacts with metals present in the catalyst such as, iron, nickel,aluminum or molybdenum to form mixed metal vanadates. These vanadatescause loss of both catalyst surface area and attrition resistance. Thisprocess is accelerated as the temperature approaches the relatively lowmelting point of the V₂ O₅ pentoxide, which is 1250° F.

Sulfation of the alumina support by sulfur trioxide formed during thecoke-burn has also been proposed as a mechanism leading tocatalyst-softening during regeneration. Vanadium pentoxide, an activeoxidation catalyst, is formed during regeneration and could catalyze theformation of sulfur trioxide from the dioxide, enhancing the aluminasulfation process.

In any event, it is postulated that when a Group VIB metal is added tothe catalyst in accordance with the present invention, prior to thefinal coke-combustion step the Group VIB metal immobilizes vanadiumpentoxide formed during regeneration. This does two beneficial things:

1. It reduces the activity of V₂ O₅ as an SO₂ -oxidation catalyst, thuspreventing formation of aluminum sulfate.

2. It limits the ability of V₂ O₅ to flux on the catalyst surface athigh decoking temperatures, thus preserving catalyst pore structure.

The above-impregnated spent catalyst is then subjected to another finaldecoking or oxidation step wherein the catalyst is contacted with anoxygen-containing gas as in the initial coke-burning step at about 600°F. to about 1,400° F. Preferably, the upper temperature limit is about1200° F. and most preferably, the upper temperature limit is about 1000°F. This step is carried out until about 95 percent or more of the cokeis removed from the catalyst.

The regenerated catalyst can then be placed back in service in ahydroprocessing process as described above. Preferably, the catalyst isintroduced into the most upstream portion of a series of ebullated bedreactors.

The operating conditions for the hydroprocessing of heavy hydrocarbonstreams, such as petroleum hydrocarbon residua and the like, comprise ahydrogen partial pressure within the range of about 1,000 psia (68 atm)to about 3,000 psia (204 atm), an average catalyst bed temperaturewithin the range of about 700° F. (371° C.) to about 850° F. (454° C.),a liquid hourly space velocity (LHSV) within the range of about 0.1volume of hydrocarbon per hour per volume of catalyst to about 5 volumesof hydrocarbon per hour per volume of catalyst, and a hydrogen recyclerate or hydrogen addition rate within the range of about 2,000 standardcubic feet per barrel (SCFB) (356 m³ /m³) to about 15,000 SCFB (2,671 m³/m³). Preferably, the operating conditions comprise a hydrogen partialpressure within the range of about 1,200 psia to about 2,800 psia(81-190 atm); an average catalyst bed temperature within the range ofabout 730° F. (387° C.) to about 820° F. (437° C.); and a LHSV withinthe range of about 0.15 to about 2; and a hydrogen recycle rate orhydrogen addition rate within the range of about 2,500 SCFB (445 m³ /m³)to about 10,000 SCFB (890 m³ /m³).

If the regenerated catalyst of the present invention were to be used totreat hydrocarbon distillates, the operating conditions would comprise ahydrogen partial pressure within the range of about 200 psia (13 atm) toabout 3,000 psia (204 atm); an average catalyst bed temperature withinthe range of about 600° F. (315° C.) to about 800° F. (426° C.); a LHSVwithin the range of about 0.4 volume of hydrocarbon per hour per volumeof catalyst to about 6 volumes of hydrocarbon recycle rate or hydrogenaddition rate within the range of about 1,000 SCFB (178 m³ /m³) to about10,000 SCFB (1,381 m³ /m³). Preferred operating conditions for thehydroprocessing of hydrocarbon distillates comprise a hydrogen partialpressure within the range of about 200 psia (13 atmos) to about 1,200psia (81 atmos); an average catalyst bed temperature within the range ofabout 600° F. (315 ° C.) to about 750° F. (398° C.); a LHSV within therange of about 0.5 volume of hydrocarbon per hour per volume of catalystto about 4 volumes of hydrocarbon per hour per volume of catalyst; and ahydrogen recycle rate or hydrogen addition rate w1th1n the range ofabout 1,000 SCFB (178 m³ /m³) to about 6,000 SCFB (1,068 m³ /m³).Generally, the process temperatures and space velocities are selected sothat at least 30 vol.% of the feed fraction boiling above 1,000° F. isconverted to a product boiling below 1,000° F. and more preferably sothat at least 60 vol.% of the subject fraction is converted to a productboiling below 1,000° F.

The present invention is described in further detail in connection withthe following examples, it being understood that the same are forpurposes of illustration and not limitation.

EXAMPLE 1

In the present example several tests were carried out to show theimprovements afforded by the invention hydroprocessing catalystregeneration process. These improvements included a restoration ofinitial catalyst activity as explained below and the achievement of anacceptable catalyst attrition rate.

In the present example, a fresh resid hydrodemetallation (HDM)hydroprocessing catalyst was compared with an invention regeneratedhydrodesulfurization (HDS) catalyst. The fresh resid HDM catalyst is acommercially available catalyst that is typically or preferably used inthe first stage of a two-stage resid hydrotreating unit, or in a moreupsteam region of a resid hydrotreating unit. The catalyst employed inthe relative upstream region should possess relatively higherhydrodemetallation and Ramscarbon removal activities since the rate ofhydrodenitrogenation and hydrodesulfurization increases furtherdownstream in the reactor. Thus, at a minimal, any catalyst regeneratedby the process of the invention should possess the demetallation andRamscarbon removal activities of a fresh HDM catalyst used in the moreupstream portion of the reactor, especially since regenerated catalystwill generally be introduced into the upstream portion of the reactor.The properties of the fresh HDM control catalyst, denoted as catalyst"A", are set out below in Table I.

The invention regenerated HDS catalyst was obtained by regenerating aspent commercial resid hydroprocessing catalyst that had been removedfrom the downstream bed of a commercial resid hydroprocessing unit.Prior to contact with feedstock at reaction conditions, the fresh HDScatalyst, denoted as catalyst "B", had properties as set out below inTable I. Prior to regeneration, the spent HDS catalyst, denoted ascatalyst "C" with the properties set out below in Table I, was washedwith toluene and hexane to strip off excess oil and dried overnight in anitrogen-purged convection oven at 250° F.

The invention regenerated HDS catalyst, denoted as catalyst "D" with theproperties set out below in Table I, was obtained by carrying out theregeneration process in accordance with the present invention. Theabove-described spent catalyst was first subjected to a partial decokingstep in the presence of air. Specifically, a large muffle furnace wasemployed wherein the temperature was increased from 300° to 600° F. at100° F. per hour increments and then held at 600° F. for 1 hour. Thispartial decoking step removed about 50 percent of the deposited coke andincreased the pore volume from about 0.1 to about 0.4 cc/g. Thepartially decoked catalyst was then impregnated with an aqueous solutionof ammonium heptamolybdate to achieve about 3.5 wt.% additional MoO₃loading on the catalyst, based on fresh catalyst weight. The subjectcatalyst was then dried overnight in an air-purged convection oven. Afinal decoking or coke-burning step was carried out in the presence ofair at 900° F. for about 2 hours after carrying out a temperatureincrease procedure from 300° to 900° F. wherein the temperature wasincreased approximately 100° F. per hour.

                  TABLE I                                                         ______________________________________                                                                       "C"    "D"                                                  "A"               Equili-                                                                              Regene-                                              Fresh    "B"      brium  rated                                                HDM      Fresh    HDS    HDS                                     Catalyst     Control  HDS      Spent  Invention                               ______________________________________                                        Chemical Analyses                                                             (wt %, Fresh Basis, Al-Tie)                                                   Ni           --       --       1.64   1.95                                    V            --       --       6.09   5.53                                    Fe           --       --       1.15   1.06                                    Na            0.031   --       0.26   0.20                                    Si           1.01     --       0.21   0.29                                    CoO          0.55     3.74     3.51   4.11                                    MoO.sub.3    3.81     15.0     15.4   18.8                                    C            --       --       54.10  0.00                                    H            --       --       2.51   0.92                                    S            0.12     --       8.02   1.50                                    Al (Fresh Basis)                                                                           (58.0)   (43.6)   (43.6) (43.6)                                  Al (Decoked Basis)                                                                         --       --       --     26.4                                    Al (Spent Basis)                                                                           --       --       25.0   --                                      Physical Inspections                                                          (Fresh Basis, Al-Tie Point)                                                   N.sub.2 Desorption                                                            BET, m.sup.2 /g                                                                            194      326      18.5   285                                     BJH, 1200 Å-, cc/g                                                                     0.80     .sup.   0.83.sup.(1)                                                                    0.073 0.72                                    Hg Porosimetry                                                                             0.24     0.24     0.21   0.37                                    PV, 1200 Å+, cc/g                                                         ______________________________________                                         .sup.(1) 2500 style N.sub.2 desorption                                   

Activity testing was carried out in a two-stage fixed-bed upflow reactorat conditions including 790° F., 0.6 LHSV, 9000 SCFB hydrogencirculation rate, and 2,000 psig total pressure. For both the freshcatalyst run and the invention run, the first upstream reactor contained13 cc of catalyst and the second downstream reactor contained 7 cc ofcatalyst. The reactor catalyst loadings were also diluted with 13 and 7cc of alundum, respectively, in order to achieve an appropriate"thermal-to-catalytic" ratio.

The thermal-to-catalytic ratio of the two-reactor system wasapproximately one. The thermal-to-catalytic ratio is calculated for aparticular reactor as the following quotient. In particular, thenumerator is the total internal volume in the thermal zone of a reactorminus the settled volume of the catalyst charge (i.e., catalyst plusdiluent) plus the interstitial liquid volume between particles in thecatalyst charge present in the reactor plus the liquid volume in thecatalyst pores. The denominator is the settled volume of the catalystitself in the catalyst charge.

The feedstock used in each test was a vacuum resid whose properties areset out below in Table II.

                  TABLE II                                                        ______________________________________                                        FEED INSPECTION                                                               Total Liquid                                                                  ______________________________________                                        Gravity, °API                                                                            7.7                                                         1000° F.+, wt %                                                                          65.2                                                        Ni, ppm           40                                                          V, ppm            170                                                         Fe, ppm           4                                                           S, wt %           2.68                                                        N, wt %           0.449                                                       O, wt %           0.61                                                        C, wt %           83.91                                                       H, wt %           10.26                                                       Ramscarbon, wt %  13.3                                                        NMR-C.sub.A, atom %                                                                             30.6                                                        1000° F.+                                                              Oils, wt %        22.0                                                        Resins, wt %      66.4                                                        Asphaltenes, wt % 11.6                                                        ______________________________________                                    

FIGS. 1 through 4 depict desulfurization activity, hydrodenitrogenationactivity, Ramscarbon removal activity, and devanadation activity,respectively, versus weight percentage accumulation of nickel plusvanadium upon the catalyst for both of the tested catalysts. Thesefigures contain the activity data measured in connection with thetesting of the respective catalysts as described above.

Denitrogenation activity was calculated assuming pseudo-first-orderkinetics with an activation energy of 45,400 Btu/lb-mol in accordancewith the following equation: ##EQU1## ps where: A_(N) is HDN activity

N_(F) is feed nitrogen content, ppm

N_(P) is product nitrogen content, ppm

LHSV is liquid (volumetric) hourly space velocity, hr⁻¹

K_(N) is pre-exponential feed nitrogen factor=82 hr⁻¹ psig⁻¹

P is total pressure, psig

E is activation energy 45,400 Btu/lb-mol

T is absolute average temperature, °R,

Devanadation activity was calculated on the basis of the followingfirst-order rate equation, where the activation energy was 83,300Btu/lb-mol: ##EQU2## where A_(v) is devanadation activity

V_(P) is product vanadium content, ppm

V_(F) is feed vanadium content, ppm

K_(v) is pre-exponential feed vanadium factor (2520×10⁶ hr⁻¹ psig⁻¹)

P is total pressure, psig

T is absolute average temperature, °R,

E is activation energy, 83,300 Btu/lb-mol

LHSV is liquid (volumetric) hourly space velocity, hr⁻¹

Desulfurization activity assuming pseudo-second order with an activationenergy of 83,300 BTU/lb-mol was calculated in accordance with thefollowing equation: ##EQU3## where: A_(s) is desulfurization activity

k_(s) is pre-exponential feed sulfur factor (2085×10⁶ hr⁻¹ psig⁻¹ /wt%)

S.sub. P 1s product sulfur content, wt%

P is total pressure, psig

S_(F) is feed sulfur content, wt%

T is absolute average temperature, ° R.,

E is activation energy, 83,300 Btu/lb-mol LHSV is liquid (volumetric)hourly space velocity, hr⁻¹

Ramscarbon removal activity assuming pseudo-second-order kinetics withan activation energy of 83,300 BTU/lb-mol was calculated in accordancewith the following equation: ##EQU4## where A_(r) is ramscarbon removalactivity

k_(r) is pre-exponential feed ramscarbon factor (130×10⁶ hr⁻¹ psig⁻¹/wt%)

R_(P) is product ramscarbon content, wt%

R_(F) is feed ramscarbon content, wt%

P is total pressure, psig

T is absolute average temperature, °R,

E is activation energy, 83,300 Btu/lb-mol

LHSV is liquid (volumetric) hourly space velocity, hr⁻¹

FIGS. 1 through 4 clearly show that all of the initial activities of theinvention regenerated HDS catalyst are equal to or exceed the fresh HDMcatalyst activities. Further, the deactivation rates were also similarfor the invention and fresh catalysts.

EXAMPLE 2

The present example serves to show the improvement afforded by theinvention regeneration process with respect to attrition resistance. Aspent catalyst whose properties are set out above in Table I wasregenerated in accordance with the invention. The subject catalyst waspartially decoked at 600° F., followed by impregnation with an aqueoussolution of ammonium heptamolybdate in an amount sufficient to yieldabout 3.5 wt.% additional MoO₃ loading on the catalyst, calculated on afresh catalyst basis. The catalyst was then fully decoked at 900° F.using the same procedure described in Example 1.

A comparative regenerated catalyst was prepared by decoking the spentcatalyst described in Example 1 in the presence of air at 900° F. for 2hours.

Each catalyst sample was passed over a U.S. 30 mesh size sieve to removefines. Subsequently, the sample was calcined for 1 hour at 900° F. in anitrogen purged oven at 6.8 SCFH using a wire mesh basket. The samplewas then cooled to room temperature in a desiccator. Each sample weight,W(b), was then recorded. Each sample was then placed in an abrasion testdrum as described in ASTM method D4058. Also loaded into the drum was a1 ml. vial of Darco G-60 activated carbon powder (100-325 mesh) tocontrol any static electricity charge build-up.

Prior to loading, the activated carbon was dried in nitrogen (0.34 SCFH)at 750° F. for 1 hour. The total weight of added carbon was about 0.4 toabout 0.5 g. The drum was then rotated at 60 rpm for 22 hours. Afterrotation, each sample was screened over a 30 mesh sieve. The screenedsample was then put into an air-purged oven at 600° F. The temperaturewas then increased to 900° F. and then held there for at least 1 hour.The oven was then cooled to 800° F. and the sample was then placed in anempty desiccator to cool. Each sample was then weighed, and the weightW(a) recorded.

The loss on attrition (LOA) was then calculated for each sample inaccordance with the following formula: ##EQU5##

An acceptable loss on attrition rate is less than about 3.0 wt.%/day andmost preferably less than about 2.5 wt.%/day. The invention regeneratedcatalyst achieved a dry loss on attrition of 2.55 wt.%/day, well belowthe acceptable rate of 3.0 wt.%/day. Several attrition tests carried outupon the comparative regenerated catalysts yielded dry loss on attritionvalues of 4.50, 4.92, 4.41, 6.14 wt.%/day.

What is claimed is:
 1. A process for regenerating a metals contaminatedheavy hydrocarbon hydroprocessing catalyst with a total contaminantmetals buildup of greater than about 4 wt.% nickel plus vanadium basedon the total weight of fresh catalyst wherein said spent catalyst priorto being deactivated by contact with a hydrocarbon stream possessed atleast 0.05 cc/g pore volume in pores having pore diameters greater thanabout 1200 Angstroms consisting essentially of the steps:a) partiallydecoking said catalyst in an initial coke-burning step wherein saidcatalyst is contacted with an oxygen-containing gas at a temperatureranging from about 400° F. to about 700° F.; b) incorporating at leastone Group VIB metal with said partially decoked catalyst, such that saidpartially decoked catalyst contains from about 0.1 to about 20.0 wt.% ofsaid Group VIB metal calculated as the oxide and based on the freshweight of said spent catalyst; and c) decoking said Group VIBmetal-containing catalyst in a final coke-burning step wherein saidGroup VIB metal-containing catalyst is contacted with anoxygen-containing gas at a temperature of about 600° F. to about 1400°F.
 2. The process of claim 1 wherein said final coke-burning step iscarried out at a temperature ranging from about 600° F. to about 1200°F.
 3. The process of claim 1 wherein said final coke-burning step iscarried out at a temperature ranging from about 600° F. to about 1000°F.
 4. The process of claim 1 wherein said Group VIB metal is molybdenum.5. The process of claim 1 wherein said partially decoked catalystcontains about 0.5 to about 10.0 wt.% of said Group VIB metal.
 6. Theprocess of claim 1 wherein said partially decoked catalyst containsabout 1.0 to about 5.0 wt.% of said Group VIB metal.
 7. The process ofclaim 1 wherein said initial coke-burning step is carried out until upto about 70 wt.% of the coke present in said spent catalyst is removed.8. The process of claim 1 wherein said spent catalyst prior to beingdeactivated by contact with a hydrocarbon stream possessed at least 0.1cc/g pore volume in pores having pore diameters greater than about 1200Angstroms.
 9. The process of claim 1 wherein said spent catalyst priorto being deactivated by contact with a hydrocarbon stream possessed apore volume of about 0.15 to about 0.3 cc/g in pores having a diametergreater than about 1200 Angstroms.